Electronic dispensers for dispensing any manner of metered doses of a liquid are well known in the art. Such dispensers are commonly used to dispense soap, lotions, disinfectants, and the like in public facilities, especially restaurants, hospitals, businesses, and so forth. These dispensers are typically “hands-free” systems wherein a sensor detects the presence of person's hands adjacent the dispenser and, in response, a controller causes a motor to automatically start and engage a pump actuating mechanism to dispense a metered dose of the liquid into the person's hands. In normal operations, the motor and pump actuating mechanism operate over a cycle wherein the motor is de-energized when the pump actuating mechanism (or an associated linkage or other member that moves with the pump actuator) returns to a “home” position that is detected by a sensor in communication with the controller. The “home” position is the closed position of the pump actuating mechanism wherein the liquid is prevented from draining or leaking from the reservoir.
An undesirable condition results, however, when any one or combination of malfunctions result in a motor jam or overrun condition, or a jam of the pump actuating mechanism in mid-cycle. When this happens, liquid may leak or even drain completely from the reservoir. For example, if the sensor that detects the home position of the pump actuating mechanism fails, the motor will continue to run and cycle the pump actuating mechanism. In another malfunction, the motor or moving members of the pump actuating mechanism may become jammed by debris or other obstruction during a dispense cycle, wherein the liquid is then free to flow from the reservoir through the open pump mechanism.
Proposals have been suggested to address (at least in part) the problem discussed above. For example, U.S. Pat. No. 8,646,655 describes a control method for a liquid soap dispenser wherein a stalled pump mechanism is reset to the “loading” position by reversing the pump motor upon detection that the pump actuator is still dispensing after a defined time period as measured by a run timer. A sensor is used to determine when the pump mechanism has returned to the loading position. Thus, this control method is premised on a maximum run time function of the motor, which times the actuation of the pump, to detect whether a stall of the pump mechanism has occurred.
U.S. Pat. No. 8,651,329 describes another control method for a liquid soap dispenser by wherein a stalled pump mechanism is reset to the loading position by reversing the pump motor. With this method, motor current is monitored during the dispense cycle and the motor is reversed if the current exceeds a predetermined level. Reversal of the motor is stopped when a sensor detects that the pump actuator has returned to the loading position.
The present invention provides an alternative solution whereby the control method considers multiple variables to determine a stall or jam of the pump mechanism before reversing the motor pump to return the pump mechanism to its home position.